>it’s the choices that Japanese people make within this environment that are healthy.

Precisely that they don't need to make choices due to their environment is what makes the difference. In the US and EU people love their individualism, spend a gazillion on fitness interventions and most people are overweight, it's probably the most visible sign of the importance of culture. As Russ Ackoff said, the correct way to address problems is not to solve them, but to dissolve them. Not to fix individual issues but to create conditions under which they do not occur.

The best way to lose weight is actually to move to a place that's full of thin people, not "do" anything. It's funny that the reverse is common wisdom, everyone who moves to an unhealthy place will always proclaim how they gained 20 pounds immediately